is-number is a project by John Schlinkert. John has a background in sales and marketing before he became an open source programmer and started creating these types of single function packages. So far he has about 1400 projects. Not all of them are this small, though many are.
He builds a lot of very basic functionality packages. Get the first n values from an array. Sort an array. Set a non-enumerable property on an object. Split a string. Get the length of the longest item in an array. Check if a path ends with some string. It goes on and on.
If you browse through it’s not uncommon to find packages that do nothing but call another package of his. For example, is-valid-path provides a function to check if a windows path contains any invalid characters. The only thing it does is import and call another package, is-invalid-path, and inverses its output.
He has a package called alphabet that only exports an array with all the letters of the alphabet. There’s a package that provides a list of phrases that could mean “yes.” He has a package (ansi-wrap) to wrap text in ANSI color escape codes, then he has separate packages to wrap text in every color name (ansi-red, ansi-cyan, etc).
To me, 1400 projects is just an insane number, and it’s only possible because they are all so trivial. To me, it very much looks like the work of someone who cares a lot about pumping up his numbers and looking impressive. However the JavaScript world also extolled the virtues of these types of micro packages at some point so what do I know.
The basic problem is that identifiers can be either types or variables, and without a keyword letting you know what kind of statement you’re dealing with, there’s no way of knowing without a complete identifier table. For example, what does this mean:
If foo is a type, that is a pointer declaration. But if it’s a variable, that’s a multiplication expression. Here’s another simple one:
foo(bar);Depending on how foo is defined, that could be a function call or a declaration of a variable bar of type foo, with some meaningless parentheses thrown in.
When you mix things together it gets even more crazy. Check this example from this article:
foo(*bar)();Is bar a pointer to a function returning foo, or is foo a function that takes a bar and returns a function pointer?
letandfnkeywords solve a lot of these ambiguity problems because they let the parser know what kind of statement it’s looking at, so it can know whether identifiers in certain positions refer to types or variables. That makes parsing easier to write and helps give nicer error messages.